Gamma

Gamma

Gamma radiation is very short wavelength, high frequency,electromagnetic radiation. This is similar to other types of electromagnetic radiation, such as visible light and X-rays, which can travel long distances.

Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.

Gamma

Gamma radiation is very short wavelength, high frequency,electromagnetic radiation. This is similar to other types of electromagnetic radiation, such as visible light and X-rays, which can travel long distances.

Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.

Alpha

Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises twoprotons and two neutrons.

Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a human hand.

Alpha particles are positively charged, This means that alpha radiation can be deflected by electric fields.

Alpha radiation can also be deflected by magnetic fields.

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Beta

Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind in the nucleus.

Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.

Beta particles move in magnetic fields they experience a deflecting force - provided their motion is not parallel to the field.

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Beta

Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind in the nucleus.

Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.

Beta particles move in magnetic fields they experience a deflecting force - provided their motion is not parallel to the field.

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Charge and

Electric current is the rate of flow of electric charge. No current can flow if the circuit is broken - for example, when a switch is open.

An electric current flows when electrons move through a conductor, such as a metal wire. Metals are good conductors of electricity.

Electricity passes through metallic conductors as a flow of negatively charged electrons. The electrons are free to move from one atom to another. We call them a sea of delocalised electrons.

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Parallel Circuit

Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel. The total amount of current flowing into the junction, or split, is equal to the total current flowing out. The current is described as being conserved.

A circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light.

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Series Circuit

Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows through each component connected in series is the same.

A circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light.

Series circuits are useful if you want a warning that one of the components in the circuit has failed. For example, a circuit breaker orfuse must be connected in series in order for it to work. If Christmas tree lights all go out when one bulb breaks, they are connected in series.

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A.C. And D.C.

If the current constantly changes direction it is called alternating current, or AC. Mains electricity is an AC supply. The UK mains supply is about 230 V. It has a frequency of 50 Hz, which means that it changes direction and back again 50 times a second. The diagram shows an oscilloscope screen displaying the signal from an AC supply.

If the current flows in only one direction it is called direct current, or DC. Batteries and solar cells supply DC electricity. A typical battery may supply 1.5 V. The diagram shows an oscilloscope screen displaying the signal from a DC supply.

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Calculating Current

Current was originally defined as the flow of charges from positive to negative. Scientists later discovered that current is actually the flow of negatively charged electrons, from negative to positive. They termed the original definition ‘conventional current’ so as not to confuse it with the newer definition of current.

The size of an electric current shows the rate of flow of electric charge. You can calculate the size of a current using this equation:

Equation: current in amps = charge(C)/time(S)

or:

Equation: I = frac{Q}{t}

where:

I is the current in amperes (amps), A

Q is the charge in coulombs, C

t is the time in seconds, s

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Potential Difference

A potential difference across an electrical component is needed to make an electric current flow in it. Cells or batteries often provide the potential difference needed.

Potential difference is often called voltage. It is also known as electromotive force. Note that this is not really a ‘force’, and it is measured in volts (not newtons).

Potential difference is measured in volts, V

The potential difference across a component in a circuit is measured using a voltmeter

The voltmeter must be connected in parallel with the component

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Resistance

Here is a resistance to the flow of an electric current through most conductors.

The resistance in a wire increases as:

The length of the wire increases

The thickness of the wire decreases

An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance.

The resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through. The relationship between resistance and wire length is proportional.

The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current. The relationship between resistance and the area of the cross section of a wire is inversely proportional.